The present invention is more particularly concerned with devices of this type which have a fastener penetrating depth adjusting assembly, such as disclosed in U.S. Pat. No. 4,767,043. The depth adjusting assembly disclosed therein interconnects upper and lower structures of the work contact assembly and is constructed and arranged to be manually adjusted to change the relative positions of said upper and lower structures between (1) a first position of adjustment wherein a work contact element at the lower end of the lower structure when the work contact assembly is in an operative position extends from a nosepiece structure a first extent and a fastener driven into a workpiece by the fastener driving element has a minimum workpiece penetration and (2) a second position of adjustment wherein the work contact element when the work contact assembly is in the operative position thereof extends from the nosepiece structure a second extent and a fastener driven into a workpiece by the fastener driving element has a maximum workpiece penetration.
The specific depth adjusting assembly disclosed in the '043 patent includes a rotary adjusting member having a notched periphery cooperable with a spring locking arm so that when engaged with a notch in the periphery of the rotary adjusting member, the rotary adjusting member is securely held or locked against rotation. The spring locking arm is biased into locking relation in response to the pivotal movement of a guard member into an operative position shielding the rotary adjusting member against manual engagement. When the guard member is pivoted into an open position allowing convenient manual access to the rotary adjusting member, the locking arm is moved out of locking engagement with the rotary adjusting member allowing free manual movement thereof. The arrangement of the '043 patent is quite effective in operation but the provision of the guide member adds cost to the assembly.
U.S. Pat. No. 5,685,473 discloses a depth adjusting assembly for accomplishing the same result. In the arrangement disclosed in the '473 patent, the rotary adjusting member is free to rotate except when the work contact assembly is in fully engaged relation with the workpiece. The operation is achieved by providing a yieldingly releasable lock on the frame structure which moves into locking relation to the otherwise freely rotatable adjusting member when the work contact assembly is moved into engagement with the workpiece. The arrangement of the '473 patent obviates the cost of the guard provided in the '043 patent arrangement but leaves the rotary member free to inadvertent and accidental movement anytime the device is being handled.
U.S. Pat. No. 5,685,473 discloses a depth adjusting mechanism which includes a turnable member, however, the turnable member is constructed and arranged to be moved out of and into an indexing pin carried by the frame structure as the work contacting structure is moved into and out of contact with the workpiece. This arrangement enables the turnable member to be accidentally moved out of the desired adjustment position as the device is being portably moved around and handled.
Other patents, such as U.S. Pat. Nos. 5,385,286 and 5,564,614, illustrate depth adjusting assemblies in which springs are provided to yieldably maintain a rotary adjusting member in any desired position of adjustment. In general, these arrangements do not utilize the cost effective arrangement of the '473 patent wherein the configuration of the exterior periphery is made to serve (1) to aid in manual movement and (2) cooperate with the spring bias.